The biliary tree is an anatomical path that transports bile secreted from the liver to the duodenum of the small intestine. The bile empties into the duodenum at the duodenal papilla. Problems occurring in the biliary tree, such as the formation of bile duct stones or papillary stenosis, are treated using medical devices that are delivered into the biliary tree. In order to access the biliary tree, the medical devices must pass through the sphincter of Oddi, a muscular valve surrounding the papilla that controls the flow of pancreatic juices and bile into the duodenum. The sphincter of Oddi is constrictive in nature, making passage through the sphincter of Oddi difficult. In order to ease passage through the sphincter of Oddi, the sphincter muscle is cut through a medical procedure called a sphincterotomy.
A sphincterotomy is performed using a medical device called a sphincterotome. An example of a sphincterotome is found in United States Patent Application Publication No. 2009/0043259, and is incorporated herein by reference. A sphincterotome comprises an elongate tubular member with a plurality of lumens extending therethrough. Typically, a cutting wire that is used to cut the sphincter muscle is disposed within one of the lumens. In addition, a wire guide is disposed within another lumen, and a third lumen may be used to inject contrast at the cutting site.
The cutting wire is disposed within one of the lumens except at a distal portion of the tubular member. At the distal portion, the cutting wire is exposed outside of the lumen and along the tubular member. The portion of the cutting wire outside of the lumen, called the cutting edge, is used to cut the sphincter muscle.
A sphincterotomy generally involves a two-part process: cannulation of the biliary tree and cutting the sphincter muscle by sending an electric current through the cutting wire (i.e, electrocautery). Cannulation of the biliary tree involves inserting the distal portion of the tubular member into the papilla and using the distal portion and the cutting edge to lift the upper portion (i.e., the roof) of the papilla. In particular, after the distal portion is inserted into the papilla, the roof of the papilla is lifted by proximally pulling the cutting wire taut. Proximally pulling the cutting wire taut causes the distal portion of the tubular member to bow and form an arc. The cutting edge, being taut, forms a secant of the arc and lifts the roof of the papilla.
Lifting the roof of the papilla, as opposed to moving other portions of the papilla, is optimal for cannulating the biliary tree because the cutting edge and the distal portion can enter the biliary tree without injuring the duodenal wall or pancreatic duct. Accordingly, the distal portion of the tubular member is inserted into the papilla with the cutting edge radially extending upward because ideally, the distal portion curls in the direction in which the cutting edge radially extends. However, in practice, the distal portion may not curl in the direction that the cutting edge faces. The size, shape, and position of the lumens within the tubular member affect the center of moment of the tubular member and ultimately the curling direction of the distal portion. As a result, even if the distal portion is inserted into the papilla with the cutting edge facing upward, the distal portion may not curl upward to lift the roof of the papilla when the cutting wire is proximally pulled.